linux-kernel - Re: [RFC][PATCH] ima: Add support for staging measurements for deletion

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Message-ID: <d48d2f37-2c38-45ff-b161-6bb68536f840@linux.microsoft.com>
Date: Thu, 11 Dec 2025 10:06:34 -0800
From: steven chen <chenste@...ux.microsoft.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>,
 Gregory Lumen <gregorylumen@...ux.microsoft.com>
Cc: corbet@....net, zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
 eric.snowberg@...cle.com, paul@...l-moore.com, jmorris@...ei.org,
 serge@...lyn.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
 nramas@...ux.microsoft.com, Roberto Sassu <roberto.sassu@...wei.com>,
 steven chen <chenste@...ux.microsoft.com>
Subject: Re: [RFC][PATCH] ima: Add support for staging measurements for
 deletion

On 12/11/2025 7:24 AM, Roberto Sassu wrote:
> On Thu, 2025-12-11 at 15:50 +0100, Roberto Sassu wrote:
>> On Thu, 2025-12-11 at 10:56 +0100, Roberto Sassu wrote:
>>> On Wed, 2025-12-10 at 11:12 -0800, Gregory Lumen wrote:
>>>> Roberto,
>>>>
>>>> The proposed approach appears to be workable. However, if our primary goal
>>>> here is to enable UM to free kernel memory consumed by the IMA log with an
>>>> absolute minimum of kernel functionality/change, then I would argue that
>>>> the proposed Stage-then-delete approach still represents unnecessary
>>>> complexity when compared to a trim-to-N solution. Specifically:
>> The benefit of the Stage-then-delete is that you don't need to scan the
>> IMA measurements list in advance to determine what to trim, you just
>> trim everything by swapping list head (very fast) and then you can read
>> and delete the measurements out of the hot path.
> I forgot: I will also add in my patch the ability to stage and trim in
> one step, to satisfy your use case.
>
> Roberto

Hi Roberto,

The below is what you want in one step. I think anything more than this 
does not bring any extra value.

I released version 2 of trim N entries patch as bellow:

[PATCH v2 0/1] Trim N entries of IMA event logs
<https://lore.kernel.org/linux-integrity/20251210235314.3341-1-chenste@linux.microsoft.com/T/#t>


Steven

>> [...]
>>
>>>> - There exists a potential UM measurement-loss race condition introduced
>>>> by the staging functionality that would not exist with a trim-to-N
>>>> approach. (Occurs if a kexec call occurs after a UM agent has staged
>>>> measurements for deletion, but has not completed copying them to
>>>> userspace). This could be avoided by persisting staged measurements across
>>>> kexec calls at the cost of making the proposed change larger.
>>> The solution is to coordinate the staging with kexec in user space.
>> To avoid requiring coordination in user space, I will try to see if I
>> could improve my patch to prepend the staged entries to the current
>> measurement list, before serializing them for kexec().
>>
>> Roberto